Quantification of Aircraft Engine Hydrocarbon Emissions Using Proton Transfer Reaction Mass Spectrometry

A proton transfer reaction mass spectrometer was used to measure the concentrations of selected volatile organic compounds in the exhaust of a commercial turbofan aircraft engine. Nine different compounds including methanol, acetaldehyde, acetic acid, benzene, toluene, phenol, styrene, naphthalene, and the methylnaphthalenes were identified as engine exhaust components that are free of spectral interferences and quantifiable by the proton transfer reaction mass spectrometer. The emission characteristics of the engine were examined as a function of engine power, fuel composition, and downstream distance from the engine. The hydrocarbon emission indices were found to be highly variable, upwards to a factor of 10 for the same nominal engine power setting. Although the magnitude of the HC emissions exhibited large variation, we observed that plots of the HC emission indices versus that of the emission index determined for formaldehyde (normalized plots) were linear and essentially independent of power setting and fuel composition, which suggests that the HC emissions scale together. The results of this study are critically examined and are shown to compare favorably with those of previous studies and serve to validate the proton transfer reaction mass spectrometer method as a reliable quantitative technique for online monitoring of selected hydrocarbon emissions within the engine exhaust matrix.